mtd: devices: elm: Low power transition support

ELM is used for locating bit-flip errors in when using BCH ECC scheme.
This patch adds suspend/resume support for leaf level ELM driver,
And also provides ELM register context save & restore support, so that
configurations are preserved across hardware power-off/on transitions.

Signed-off-by: Philip Avinash <avinashphilip@ti.com>
Signed-off-by: Pekon Gupta <pekon@ti.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/devices/elm.c

@@ -20,14 +20,21 @@
 #include <linux/interrupt.h>
 #include <linux/io.h>
 #include <linux/of.h>
+#include <linux/sched.h>
 #include <linux/pm_runtime.h>
 #include <linux/platform_data/elm.h>
 
+#define ELM_SYSCONFIG			0x010
 #define ELM_IRQSTATUS			0x018
 #define ELM_IRQENABLE			0x01c
 #define ELM_LOCATION_CONFIG		0x020
 #define ELM_PAGE_CTRL			0x080
 #define ELM_SYNDROME_FRAGMENT_0		0x400
+#define ELM_SYNDROME_FRAGMENT_1		0x404
+#define ELM_SYNDROME_FRAGMENT_2		0x408
+#define ELM_SYNDROME_FRAGMENT_3		0x40c
+#define ELM_SYNDROME_FRAGMENT_4		0x410
+#define ELM_SYNDROME_FRAGMENT_5		0x414
 #define ELM_SYNDROME_FRAGMENT_6		0x418
 #define ELM_LOCATION_STATUS		0x800
 #define ELM_ERROR_LOCATION_0		0x880
@@ -56,12 +63,27 @@
 #define SYNDROME_FRAGMENT_REG_SIZE	0x40
 #define ERROR_LOCATION_SIZE		0x100
 
+struct elm_registers {
+	u32 elm_irqenable;
+	u32 elm_sysconfig;
+	u32 elm_location_config;
+	u32 elm_page_ctrl;
+	u32 elm_syndrome_fragment_6[ERROR_VECTOR_MAX];
+	u32 elm_syndrome_fragment_5[ERROR_VECTOR_MAX];
+	u32 elm_syndrome_fragment_4[ERROR_VECTOR_MAX];
+	u32 elm_syndrome_fragment_3[ERROR_VECTOR_MAX];
+	u32 elm_syndrome_fragment_2[ERROR_VECTOR_MAX];
+	u32 elm_syndrome_fragment_1[ERROR_VECTOR_MAX];
+	u32 elm_syndrome_fragment_0[ERROR_VECTOR_MAX];
+};
+
 struct elm_info {
 	struct device *dev;
 	void __iomem *elm_base;
 	struct completion elm_completion;
 	struct list_head list;
 	enum bch_ecc bch_type;
+	struct elm_registers elm_regs;
 };
 
 static LIST_HEAD(elm_devices);
@@ -384,6 +406,100 @@ static int elm_remove(struct platform_device *pdev)
 	return 0;
 }
 
+/**
+ * elm_context_save
+ * saves ELM configurations to preserve them across Hardware powered-down
+ */
+static int elm_context_save(struct elm_info *info)
+{
+	struct elm_registers *regs = &info->elm_regs;
+	enum bch_ecc bch_type = info->bch_type;
+	u32 offset = 0, i;
+
+	regs->elm_irqenable       = elm_read_reg(info, ELM_IRQENABLE);
+	regs->elm_sysconfig       = elm_read_reg(info, ELM_SYSCONFIG);
+	regs->elm_location_config = elm_read_reg(info, ELM_LOCATION_CONFIG);
+	regs->elm_page_ctrl       = elm_read_reg(info, ELM_PAGE_CTRL);
+	for (i = 0; i < ERROR_VECTOR_MAX; i++) {
+		offset = i * SYNDROME_FRAGMENT_REG_SIZE;
+		switch (bch_type) {
+		case BCH8_ECC:
+			regs->elm_syndrome_fragment_3[i] = elm_read_reg(info,
+					ELM_SYNDROME_FRAGMENT_3 + offset);
+			regs->elm_syndrome_fragment_2[i] = elm_read_reg(info,
+					ELM_SYNDROME_FRAGMENT_2 + offset);
+		case BCH4_ECC:
+			regs->elm_syndrome_fragment_1[i] = elm_read_reg(info,
+					ELM_SYNDROME_FRAGMENT_1 + offset);
+			regs->elm_syndrome_fragment_0[i] = elm_read_reg(info,
+					ELM_SYNDROME_FRAGMENT_0 + offset);
+		default:
+			return -EINVAL;
+		}
+		/* ELM SYNDROME_VALID bit in SYNDROME_FRAGMENT_6[] needs
+		 * to be saved for all BCH schemes*/
+		regs->elm_syndrome_fragment_6[i] = elm_read_reg(info,
+					ELM_SYNDROME_FRAGMENT_6 + offset);
+	}
+	return 0;
+}
+
+/**
+ * elm_context_restore
+ * writes configurations saved duing power-down back into ELM registers
+ */
+static int elm_context_restore(struct elm_info *info)
+{
+	struct elm_registers *regs = &info->elm_regs;
+	enum bch_ecc bch_type = info->bch_type;
+	u32 offset = 0, i;
+
+	elm_write_reg(info, ELM_IRQENABLE,	 regs->elm_irqenable);
+	elm_write_reg(info, ELM_SYSCONFIG,	 regs->elm_sysconfig);
+	elm_write_reg(info, ELM_LOCATION_CONFIG, regs->elm_location_config);
+	elm_write_reg(info, ELM_PAGE_CTRL,	 regs->elm_page_ctrl);
+	for (i = 0; i < ERROR_VECTOR_MAX; i++) {
+		offset = i * SYNDROME_FRAGMENT_REG_SIZE;
+		switch (bch_type) {
+		case BCH8_ECC:
+			elm_write_reg(info, ELM_SYNDROME_FRAGMENT_3 + offset,
+					regs->elm_syndrome_fragment_3[i]);
+			elm_write_reg(info, ELM_SYNDROME_FRAGMENT_2 + offset,
+					regs->elm_syndrome_fragment_2[i]);
+		case BCH4_ECC:
+			elm_write_reg(info, ELM_SYNDROME_FRAGMENT_1 + offset,
+					regs->elm_syndrome_fragment_1[i]);
+			elm_write_reg(info, ELM_SYNDROME_FRAGMENT_0 + offset,
+					regs->elm_syndrome_fragment_0[i]);
+		default:
+			return -EINVAL;
+		}
+		/* ELM_SYNDROME_VALID bit to be set in last to trigger FSM */
+		elm_write_reg(info, ELM_SYNDROME_FRAGMENT_6 + offset,
+					regs->elm_syndrome_fragment_6[i] &
+							 ELM_SYNDROME_VALID);
+	}
+	return 0;
+}
+
+static int elm_suspend(struct device *dev)
+{
+	struct elm_info *info = dev_get_drvdata(dev);
+	elm_context_save(info);
+	pm_runtime_put_sync(dev);
+	return 0;
+}
+
+static int elm_resume(struct device *dev)
+{
+	struct elm_info *info = dev_get_drvdata(dev);
+	pm_runtime_get_sync(dev);
+	elm_context_restore(info);
+	return 0;
+}
+
+static SIMPLE_DEV_PM_OPS(elm_pm_ops, elm_suspend, elm_resume);
+
 #ifdef CONFIG_OF
 static const struct of_device_id elm_of_match[] = {
 	{ .compatible = "ti,am3352-elm" },
@@ -397,6 +513,7 @@ static struct platform_driver elm_driver = {
 		.name	= "elm",
 		.owner	= THIS_MODULE,
 		.of_match_table = of_match_ptr(elm_of_match),
+		.pm	= &elm_pm_ops,
 	},
 	.probe	= elm_probe,
 	.remove	= elm_remove,